Self-centering button-grinding apparatus of this kind are known from SE-A 8803684-3 and SE-A 8902794-0. In apparatus of this known kind, the whole of the grinding machine moves in an orbital path while being firmly attached to the rotational shaft of the rotary device. This construction creates certain problems, among other things because of the centrifugal forces to which the grinding machine is subjected, but primarily because it is necessary to provide the output shaft of the rotary device with a swivel coupling and to provide on said shaft various axially extending passages for the delivery of driving and cooling agents to the grinding machine. Another drawback with this known construction is that the rotating grinding machine constitutes a latent risk of injury to the machine operator.
Consequently, there is a strong desire to avoid these drawbacks and also to simplify the button grinding apparatus in general aspects, without departing from its self-centering function or from the ease of handling which enables the operator of such apparatus to manoeuvre the apparatus without the use of excessive force and which is characteristic of the button grinding apparatus taught by said patent specification.
An apparatus for renovating the buttons of button bits is also known from US-A 4,858,388, this apparatus including a bracket structure which can be raised and lowered along a pylon or post. The bracket is carrying a rotatable device whose shaft coacts with a drive means such as to cause a laterally mounted grinding machine to execute rocking, orbital motion. This is achieved by attaching the grinding machine to an annulus such that the drive shaft of the grinding machine will extend obliquely to the vertical line of the renovating apparatus. The annulus is rotatably journalled in the bracket and is driven by the shaft-drive of the rotatable device. The grinding machine is supported on journals in the central opening of the annulus and the grinding machine is prevented from rotating by means of an elastic coupling which couples the machine to the bracket structure.
Besides the drawback with this known apparatus in that the intrinsic weight of the apparatus and the friction generated in the bearings counteract the self-centering effect and the operator has difficulty in maneuvering the apparatus it is encumbered with a number of troublesome constructional problems, primarily caused by the lateral positioning of the grinding machine and its complicated journalling means.